1. Field of the Invention
This invention relates to line density multiplication in the area of nanotechnology, such as the fabrication of semiconductor devices and nanoimprint templates.
2. Description of the Related Art
Current photolithography has reached fundamental printing limits. One process that is gaining recognition for use in DRAM and NAND flash manufacturing is sidewall spacer “line doubling”, sometimes also referred to as “line multiplication”, “frequency doubling”, or “pitch-halving”. The process also has application in making nanoimprint templates, which may be used for making bit-patterned-media magnetic recording disks, for example as described in U.S. Pat. No. 7,758,981 B2 which is assigned to the same assignee as this application.
The process uses sidewall spacers to create patterned hardmasks as a means of doubling the printed line density. The process is illustrated in FIGS. 1A-1F. A layer of hardmask material is deposited on a substrate, and a layer of mandrel material (which may be a photoresist) is patterned into lines on the hardmask layer (FIG. 1A). A conformal layer of spacer material is deposited on the tops and sides of the mandrel lines and on the hardmask layer in the gaps between the mandrel lines (FIG. 1B). The spacer material on the tops of the mandrel lines and in the gaps between the mandrel lines is then removed by anisotropic etching, leaving the mandrel lines with sidewalls of spacer material (FIG. 1C). The material of the mandrel lines is then removed, leaving lines of sidewall spacer material on the hardmask layer (FIG. 1D). The number of spacer lines in FIG. 1D is double the number of mandrel lines in FIG. 1A, and thus the pitch of the spacer lines is half the pitch of the mandrel lines, hence the terms “line doubling” and “pitch halving”. The spacer lines are then used as an etch mask to transfer the pattern into the hardmask (FIG. 1E) and the spacer lines are then removed, leaving a pattern of hardmask lines on the substrate (FIG. 1E).
Atomic layer deposition (ALD) is one method of depositing various types of spacer materials. ALD is a thin film deposition process that is based on the sequential use of a gas phase chemical process, in which by repeatedly exposing gas phase chemicals known as the precursors to the growth surface and activating them at elevated temperature, a precisely controlled thin film is deposited in a conformal manner. Many ALD processes are “energy-assisted”, meaning that they are performed with the assistance from a plasma or ozone.
What is needed is a sidewall spacer line doubling process that uses an ALD process that enables new sets of materials for the mandrel and spacer material.